Siemens SIMATIC NET SCALANCE SC-600 - Page 42

Technical basics
3.4 VLAN
SCALANCE SC-600 Web Based Management (WBM)
42 Configuration Manual, 10/2021, C79000-G8976-C475-03
The tagged frame has 3 bits for the priority that is also known as Class of Service (CoS),
see also IEEE 802.1Q.
CoS bits
Priority
Type of the data traffic
000
0 (lowest)
Background
001
1
Best Effort
010
2
Excellent Effort
011
3
Critical Applications
100
4
Video, < 100 ms delay (latency and jitter)
101
5
Voice (language), < 10 ms delay (latency and jitter)
110
6
Internetwork Control
111
7 (highest)
Network Control
The prioritization of the data packets is possible only if there is a queue in the
components in which they can buffer data packets with lower priority.
The device has multiple parallel queues in which the frames with different priorities can
be processed. As default, first, the frames with the highest priority are processed. This
method ensures that the frames with the highest priority are sent even if there is heavy
data traffic.
Canonical Format Identifier (CFI)
The CFI is required for compatibility between Ethernet and the token Ring.
The values have the following meaning:
Value
Meaning
0
The format of the MAC address is canonical. In the canonical representation of the MAC
address, the least significant bit is transferred first. Standard-setting for Ethernet
switches.
1
The format of the MAC address is not canonical.
VLAN ID
In the 12-bit data field, up to 4096 VLAN IDs can be formed. The following conventions
apply:
VLAN ID
Meaning
0
The frame contains only priority information (priority tagged frames) and no
valid VLAN identifier.
1- 4094
Valid VLAN identifier, the frame is assigned to a VLAN and can also include
priority information.
4095
Reserved